In this project we build upon ongoing efforts of the researchers and practitioners of the HMO Research Network Center for Education and Research in Therapeutics (CERTs) and of the Kaiser Permanente Colorado Clinical Research Unit to improve medication safety in the ambulatory care environment. This project is a population-based retrospective cohort study in response to PA-05-094 (Secondary Analyses in Obesity, Diabetes, Digestive and Kidney Diseases) that uses the large existing automated record linkage systems and associated medical records of four HMO Research Network CERTs sites. This study will assess the associations between both receipt and timing of serum potassium monitoring and the occurrence of hyperkalemia-associated hospitalizations, emergency department visits, and deaths in approximately 17,000 ambulatory patients with diabetes who are newly-prescribed angiotensin converting enzyme inhibitors (ACEi), angiotensin receptor blockers (ARB), and/or aldosterone receptor antagonists (ARA). ACEi, ARB and/or ARA are important therapeutic modalities. Unfortunately, they are associated with potentially life-threatening hyperkalemia. Patients with diabetes comprise up to half of all patients prescribed these drugs and are at increased risk of hyperkalemia-associated adverse outcomes, but whether potassium monitoring helps to decrease these adverse outcomes is not clear. Results from this project will supply evidence about whether patients with diabetes who receive potassium monitoring after being newly- prescribed ACEi, ARB, and/or ARA have a lower incidence of hyperkalemia-associated adverse outcomes than patients who are not monitored. Additionally, knowledge gained will include information about patient characteristics associated with increased risks. Our intent is to use the findings from this exploratory project for future work to develop and evaluate evidence-based serum potassium monitoring recommendations for patients with diabetes who are prescribed these drugs. The findings will also assist in developing a framework for future studies to evaluate the effects and costs of medication-laboratory monitoring among patients with diabetes. [unreadable] [unreadable] [unreadable] [unreadable]